Autonomic ganglia are studied here as a relatively simple model of synaptic interactions in the vertebrate nervous system. The investigation focusses on the nature of the slow postsynaptic responses. These include slow PSP's lasting seconds to minutes, and their electrogenic processes and chemical synaptic transmitter pathways; it also includes a novel synaptic modulatory action by one transmitter on the responses to another transmitter. We have established that dopamine is not only a direct transmitter for the slow inhibitory postsynaptic response, but that it also acts to produce a long-lasting enhancement (several hours) of the slow depolarizing (excitatory) response to another transmitter, acetylcholine. We propose to analyze the nature and the physiological significance of the enduring neuronal changes induced by dopamine, which are involved in this latter type of synaptic modulation. The work should be potentially important not only to the physiology and pharmacology of the autonomic nervous system. It has already led to a possible model for enduring neuronal changes such as those in memory formation, and it is hoped that the cellular processes involved will be elaborated more fully.